Copper-cobalt-zinc alloy



Patented Aug. 16, 1938 COPPER-COBALT-ZINC ALLOY I Cyril Stanley Smith, Cheshire, Conn., assignor to The American Brass Company,

Waterbury,

Conn., a corporation of Connecticut No Drawing.

Application January 20, 1936,

Serial N 0. 59,930

8 Claims.

My invention relates to an alloy of copper, zinc and. cobalt characterized by the ductility and ready workability of the brasses yet capable of being hardened by a simple precipitation treatment which will increase the strength and yield point considerably.

The alloys of copper and zinc find very extensive application inthe arts on account of their good corrosion resistance and strength combined with a high ductility which permits them to be formed easily by the various processes of rolling, drawing, spinning, stamping, etc. I have found that additions of cobalt to the brasses in amounts upto about 8 per cent. have a slight hardening effect if the alloys are either quenched or very slowly cooled and do not reduce the ductility appreciably. On the other hand, if the alloys containing cobalt are given a simple precipitation treatment following a quench, with or without intermediate cold working, the tensile strength will be improved. without a very severe reduction of elongation and the yield point is very greatly increased.

The strength of the alloy is not extremely high and the alloy does not compete with alloys such as beryllium-copper, but it is sufficiently strong for most purposes and the ductility, even in the hardened'condition, is much higher than most other precipitation hardening alloys. For this reason, the alloys are useful in cases where considerable ductilityis desired in the finished article.

The zinc content of my alloy may range approximately from one to 45 per cent., depending on the major characteristics of the alloy desired, and cobalt should be between 1 and 8 percent.

40% zinc and 2.5% to 5.5% cobalt. An alloy within the latter range of cobalt preferably about 4% and of 30% zinc is most suitable for deep drawing operations, but 40% zinc (with same. cobalt content) will give a stronger alloy, and alloys containing in the neighborhood of 15% or less zinc (preferably about 3% cobalt) are desirable where freedom from dezincification under corrosive conditions is desired.

I have found that the solubility of cobalt varies considerably with temperature and at 'a given temperature is slightly greater in the alloys containing high zinc than it is in pure copper. For

example, 4 per cent. cobalt is soluble at 850 C. in the presence of 30 per cent. zinc and only 2 per cent. at 600 C.

The alloys may be made in the same manner 3 x as brass except for the addition of cobalt which may be made by introducing into the molten brass, or preferably to the copper before zinc is added, either metallic cobalt in a suitable form or .cent. zinc with cobalt between 2 and 5 per cent.

This shows the properties of the alloys both in the quenched condition and after a precipitation The most useful range appears to be from to treatment. I

'TABLE I r Tensile properties of copper-zinc-cobalt alloys Alloy Yield point, Tensile Elongation Rockwell No Analysis, percent; Treatment lbs. $1 in. strength, on 2 in.. perhardness 0.5 0 xt. lbsJsq. in. cent. 3" scale Copper, 00.45..-- Q.irom 850 0 12,250 43,750 00.0 0.4 1255 Zinc. 28.45 Ditto; reheated-.. 33,900 50,400 47.0 55.3

Cobalt, 2.10.. 4 hrs. at 450 C.

- Copper, 00.53 Q. irom850 c. 12,050 41,700- 46.8 1.0 mm. Zinc, 20.57 Ditto; reheated...--; 51,350 00,000 30.0 73.4 Cobalt, 3.90..." am. at 450 0. Copper, 04.00.--- Q. irom850 c 1 050 4 250 47.8 151 1232 Zinc, 31.01 Ditto; reheated"--- 00: 200 7%000 31.0 31.0

Cobalt, 4.90..." 4 hrs. at 4l50 C. I Copper, 64.33.. Q. ir0m850 C. 15,800 48,900 4 I 22.3 1283 Zinc,30.30..-.- Ditto: 1100011000---- 01,200 81,000 33.0 81.8 Cobalt,5.37 4hrs.at 450 C.

The alloy may be It will be noticed that the precipitation treat? ment increases the tensile strength considerably, while the yield point in the alloys containing sufficient cobalt is practically quadrupled. At the same time the elongation remains quite high showing that the alloys retain a large measure of their ductility. The strength of the alloys can be further increased by cold working either between the quenching and precipitation treatments or after the latter. treatment is similar in alloys containing either more or less zinc than that shown in the table, and the zinc content is selected for a given purpose on the basis of the corrosion resistance and strength and ductility required in the same manner as in the industrial brasses. lvl'icroscopically the alloys resemble in structure the brasses on which they are based but may have an additional constituent rich in cobalt. Cobalt exerts a restraining infiuence on grain growth on annealing and may sometimes be useful for this action alone. The alloys may be used either in the alpha region, in the alpha-i-beta, or even the beta region of the copper-zinc alloys, but are always characterized by cobalt additions in suflicient amount to permit precipitation hardening. v

As in all precipitation hardening alloys, it is necessary to subject the alloys to a solution heat treatment which is followed by quenching or other cooling at a sufficiently rapid rate to retain much of the excess solute in solution"; and'then to reheat at some suitable temperature where precipitation commencesfor a time suflicient to attain a suitable critical dispersion of the precipitate to result in an increase in hardness. In

- the case of the copper, cobalt, zinc alloys thesolu- -tion heat treatment should be at a temperature .above 700 C. and below the temperature at which the alloys commence to melt. perature of about 850 C. for the alloys containing 25 to 45 percent zinc, and for the alloys below 25 percent zinc a temperature of about 950 C. The maximum hardness is obtained on reheating the quenched alloys for about 4 hours at about 450 C., but treatment at a higher temperature up to about 650? C.-for an appropriate shorter time, or a lower temperature down to about 300 C. for a suitable longer time will give almost identical results. At any temperature there will be an optimum time for producing the best hardness,

and ifeither more or less time than this is given the hardness will be less than the maximum obtainable. If the alloys are cold worked between the quenching and precipitation treatments the latter must be at a somewhat lower temperature since precipitation is accelerated by cold working. The precipitation treatment may either follow the solution heat treatment directly or the alloys may becold worked between the two heat treatments, when the alloy is in its softest condition. The hardened alloy may be further cold worked if still higher strength is required.

Under some conditions it might be advisable to cool directly from the temperature of the solution heat'treatment to the temperature for the precipitation heat treatment without intermediate cooling to room temperatures, and considerable hardening may be obtained merely by cooling through the'precipitation zone at the correct rate. If

castings are cooled sufficiently rapidly after solidification, the solution heat treatment may sometimes be dispensed with. Since the alloy is very ductile either as quenched or when slowly cooled and does not become brittle at any time, it may be given intermediate'processing anneals during The effect of heat I prefer a t e mthe course of fabrication without particular attention being paid to the method of cooling. The solution heat treatment and its necessary quench need be given only at the final stage of manufacture.

The alloy may be cast in sand molds and also in permanent molds either with or without application of pressure as used in the die casting process. a

The alloy may be hot or cold rolled into plate, sheet, strip, rod, and in fact, all rolled shapes. It may be drawn through dies into rod, wire, tube, and irregular shapes. It may be forged hot or cold as in die pressing or similar forming operations. It may be extruded into simple shapessuch as bars and rods and also into the more complex forms commonly known as architectural shapes.

The alloy because of its hot and cold working properties can be used to advantage in manufacture of bolts, nuts, U-bolts, and similar articles such as lag screws and scgew productsand washers for them.

The alloy may be .soldered, welded or brazed and is thus suitable for use in production of all types of fabricated articles either by gas, electric or other welding methods, or by brazing with a suitable solder in a reducing atmosphere with- The alloy may also be used in the form of rod, wire or powder as a filler material for welding or brazing ferrous and non-ferrous materials.

.The alloy sheet, or other suitable form may be stamped, spun, pressed, or drawn into shapes such as cups, shells, diaphragms, and all forms and shapes made by such processes.

The wire or trip may be woven or otherwise formed into screens or similar products.

The alloy has good corrosion resistance, being equal to or better than copper (depending upon the corrosive agent and the method of its use) and may be used to advantage wherever corrosion resistant properties are desired with the added advantages of strength, hardness, and

wear resistance superior to copper.

The electrical properties combined with the strength, hardness and toughness of the alloy obviously suggest its use wherever such combinations of properties are desired such as for conductors for electricity in the form of wire, electrodes in resistance welding machines, switch contacts, contactors, commutator segments and other electrical uses wherein the electrical conductivity requirements are subordinate to those.

of strength and hardness. The alloy is non-magnetic.

Having thus set forth the nature, of my invention, what I claim is:

1. The treatment of, alloys containing zinc from 15 to per cent., cobalt from 1 to 8 per cent., balance copper; which comprises quenching from a temperature in excess of 700 0., cold working, and reheating at a temperature between H prises quenching the alloy from a temperature in the neighborhood of 850 C. and reheating at a temperature in'the neighborhood of 400 C. for a time suiiicient to produce a substantial increase in hardness and strength.

4. The process of improving the physical properties of an alloy containing approximately 30% zinc, 4% cobalt and balance copper, which comprises quenching the alloy from a temperature in the neighborhood of 850 6., cold working, and reheating at a temperature in the neighborhood of 400 C. for a time sufllcient to produce a substantial increase in hardness and strength.

5. An age hardened alloy comprising 15 to 45% zinc, 1 to 8% cobalt and balance copper, which has been quenched from a temperature in excess of 700 C. and aged at a temperature between 300 and 650 C. for a sumcient time to produce a substantial increase in hardness and strength.

6. An age hardened 'alloy comprising approximately 30% zinc, 4% cobalt and balance copper,

which has been quenched from a temperature in the neighborhood of 850. 0: and aged at a temperature in the neighborhood of 400 C. for a sufficient time to produce a substantial increase in hardness and strength.

7. An age hardened alloy comprising 15 to 45% zinc, 1 to 8% cobalt and balance copper, which has been quenched from a temperature in excess of 700 C., cold worked, and aged at a temperature between 300 and 650 C. for asuflicient time to produce a substantial increase in hardness and strength.

8. An age hardened alloy comprising approximately 30% zinc, 4% cobalt and balance copper, which has been quenched from a temperature in the neighborhood of 850 0., cold worked, and aged at a temperature in the neighborhood of 400 C. for a suflicient time to produce a substantial increase in hardness and strength.

CYRIL STANLEY SMITH. 

